Inkjet printing mechanisms are used in a variety of different products, such as plotters, facsimile machines and printers, collectively referred to herein as inkjet printers. These inkjet printers contain one or more inkjet printheads, also called “pens.” A printhead is fluidically coupled to a reservoir of ink. The function of the print head is to eject minute ink drops, disposed from the ink reservoir, onto a sheet of print media. To print an image, the pen is mounted to a carriage in the printer. The carriage traverses over the surface of a blank sheet of media, and the print head is controlled to eject drops of ink at appropriate times pursuant to commands from a microcomputer or other controller. The timing of the application of the ink drops corresponds to the pattern of the desired image or text to be printed.
The print head ejects the ink drops through nozzles. The particular ink ejection mechanism within the print head may take on a variety of different forms known to those skilled in the art, such as thermal print head technology. In a thermal inkjet system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains arrays of heater elements, such as resistors, which are selectively energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.
Nozzle array designs often include multiple columns of nozzles, with the nozzles in a column having a certain nozzle-to-nozzle spacing. By staggering the nozzles in different columns relative to the print media, nozzles in different columns can print on different rows of the print media, thus allowing a higher resolution image to be formed than would be possible with only a single column of nozzles with that nozzle-to-nozzle spacing.
In some applications, high printing speed may be more important than high image resolution. However, it may be difficult to achieve a desired high printing speed because the printing speed is typically limited by, among other factors, the frequency at which drops can be ejected from a given nozzle.
For these and other reasons, there is a need for the present invention.